Process and installation for the handling and heat treatment of cast iron or steel pipes and tubes

ABSTRACT

Concave rails 17, upon which a pipe which is to be treated by at least partial immersion can be placed, are fixed in the bottom of a furnace 1 which contains a treatment bath M. In order to guarantee that the pipe is immersed over the whole of its cross section and in order to eliminate the risk of it becoming oval, the furnace is subjected to alternating rotation about its axis XX, which compels the pipe to turn on itself by rolling on the rails 17. The handling of the pipe is achieved by arms 12 which are assembled in a pivoting manner on the external wall of the furnace and controlled by an actuator 15.

The present invention is concerned with the heat treatment of spheroidalor lamellar graphite cast iron pipes, which are moulded by centrifuging,and of steel tubes, and more precisely to the annealing of such productsin a metal bath of for example aluminum or an aluminium alloy.

The applicant has described a process and an installation for carryingout such a heat treatment in the French patent application filed on Mar.2nd 1977 under the number 77/06076, which is now published under thenumber 2,382,502.

The process which is known from the above patent application consists ofcausing a cast iron pipe which is immersed, partially or totally, in ametal bath, to rotate in such a manner that in all cases its entirecross section is introduced into the bath during the course of rotation.This avoids ovalisation of the pipe.

According to application 77/06076, an installation for implementing thisprocess consists of arms for suspending the pipe in a horizontalposition in the metal bath. These arms, which are equipped with carryingrollers which are positioned within the pipe but outside the bath, areassembled on hoists and are retractable when the pipe is suspended froma lifting beam above the treatment bath.

The aim of the present invention, which also implements the processrecalled above of the patent application 77/06076, is a process and aninstallation for handling and treatment of cast iron or steel pipes ortubes, which introduce a notable simplification to the handling of thepipes in order to put them into the bath and remove them from the bath,as well as for supporting them within the metal bath.

The present invention provides a process for the heat treatment of acast iron or steel pipe or tube, in which the pipe is immersed at leastpartially in a metal bath contained in a cylindrical receptacle orfurnace, and the pipe is caused to turn on itself in such a manner thatall of its cross section is completely introduced into the bath duringthe course of rotation, characterised in that the pipe is placed withinthe furnace such that it acquires, under the effect of gravity, aposition in which its external convex surface is tangential to a concavesurface of the furnace, and a reciprocating rotational movement aroundits axis is imparted to the furance, whereby the pipe is caused to turnon itself while rolling in contact with the concave surface.

Preferably, a support is positioned beneath the lower surfaces of thepipe after it leaves the rolling surface of a feed ramp which is outsidethe furnace, and the pipe is then transferred on the support directlyonto the concave surface of the furnace. Similarly, after treatment, asupport is positioned beneath the lower surfaces of the pipe which isresting on the concave surface of the furnace and the pipe is thentransferred on the support directly onto the rolling surface of anevacuation ramp which is outside the furnace and which, if necessary, iscombined with the supply ramp.

The invention also provides an installation including a receptacle orfurnace, of general cylindrical shape, containing a metal treatment bathand means for heating this bath, rollers with a horizontal axis whichsupport the furnace, handling means for introducing and removing pipesthrough an opening in the furnace, and means for imparting an angularmovement to the furnace around its horizontal axis, characterised inthat, on the internal wall of the furnace, rolling surfaces are providedwhich are directed laterally and are of concave profile, in order tosupport a pipe resting thereon.

By means of this arrangement, the immersion of the pipe into the bathover the whole of its cross section is ensured by very simple means,without risking ovalisation since the pipe is caused to rotate on itselfby rolling within the furnace.

Preferably, the handling means comprise means for retaining andtransferring a pipe, the retaining and transferring means beingarticulated on the external wall of the furnace in such a manner thatthey can penetrate within the furnace in order to place a pipe to betreated on rolling surfaces of the furnace and can be moved out of thefurnace in order to remove a treated pipe from the bath.

By means of this particular arrangement, the means for handling eachpipe are reduced to their most simple form.

Embodiments of the invention will now be described, by way of example,with reference to the accompanying drawings, in which:

FIG. 1 is a diagrammatic view, in cross section, of an installationaccording to the invention, illustrating a lateral cross section of anannealing furnace whilst a pipe to be treated is being introduced;

FIG. 2 is a diagrammatic view of the annealing furnace, in elevation,partly from the outside and partly in cross section;

FIG. 3 is a partial view of the means for gripping and transferring thepipe, which are pivoted on the external wall of the annealing furnace;

FIGS. 4 to 8 are diagrammatic views of the successive phases of handlingand treatment of a pipe inside and outside the annealing furnace, withalternating rotating or oscillating movements of the annealing furnace;

FIGS. 9 and 10 are diagrammatic views similar to FIGS. 1 and 4, of twophases of handling a pipe in an annealing furnace equipped with avariant of the internal rolling surfaces for support of the pipe;

FIGS. 11 to 13 are partial diagrammatic views of variants of means forgripping and transferring the pipe; and

FIG. 14 is a diagrammatic view which is similar to FIG. 4 of a variantof the annealing furnace according to the invention, equipped only withinternal rolling surfaces for support of the pipe.

The cylindrical annealing furnace 1, with an axis XX, includes at eitherend two annular bearing surfaces 6, each of which rests on two rotatingrollers 7, which are arranged symmetrically in relation to the verticalplane P which passes through the axis XX and are supported by aninfra-structure A which is anchored to the ground. The sheet steel wallof the furnace, which is lined on the inside with refractory bricks 2,has a longitudinal opening 3 for introducing and removing each pipe T,which a sliding cover 4 can close.

Two burners 5, whose nozzles are directed axially and are situated abovethe axis XX and in the plane P when the furnace is in the centeredposition of FIG. 1, are fixed, in a manner already known, by collars onthe end faces of the furnace 1. These burners 5 produce long flamesabove the level of the bath of metal M. As a variant, the burners 5 canbe replaced by any other equivalent means of heating, for example, byinduction heating as in the above-mentioned patent application 77/06076.

For the driving of the rotating furnace, a drive pinion 9 is providedthe axis of which is parallel to the axis XX and which is supported bythe infra-structure A. This engages with a toothed rack 8 which issupported by the external face of the steel plate wall of the annealingfurnce, for example, towards the middle of the furnace, but which may bein the vicinity of an annular bearing surface 6. This toothed rack formsan arc which is greater than the maximum amplitude of rotation of thefurnace, which is calculated in such a manner as to correspond to atleast a half turn of rotation of the pipe T in the bath M. Thisamplitude is, for example, 90°.

The pinion 9 is driven, via a transmission, by a reduction gear unit 10fixed inside the infra-structure A, for example, at the bottom of a pit.It is able to cause the furnace 1 to rotate in both directions ofrotation f and f₁ and, in particular, to impart to it an alternatingrotation which gives rise to angular movements of equal amplitude,either side of the vertical plane P starting from the centered positionof FIG. 1.

Instead of the means 8, 9 and 10 for causing the furnace 1 to oscillate,it is possible to use equivalent means, for example, two mechanisms,each of which corresponds to a direction of rotation, consisting of achain, one end of which is attached to the wall of the furnace and theother end to the stem of a traction actuator, and which is wound on areversing pinion.

For the handling of the pipe T, two gripping and transfer arms 12, whichare identical and parallel, are each pivoted, at one end about a shaft21 which is parallel to the axis XX and is mounted on a lug or flange 11which is fixed on the external face of the furnace wall in the vicinityof the lower edge of the opening 3. The arms 12 are rotated togetheraround the axis YY (FIG. 2) which is established by the shafts 21 by across piece 13, which is, for example, coaxial with the two pivot shafts21. Each arm 12 has a double curved shape, or proboscis shape,established on the internal face of the arm, in a position adjacent tothe shafts 21, by a deep concave loop 22, and as a continuation of acentral portion or branch 23 opposite the shafts 21 by a shallowexternal concavity 24, which forms an end cradle in which a pipe can beheld. The end cradle can penetrate within the furnace through theopening 3 (arrow G) when the arms 12 pivot anti-clockwise and when theloops 22 overlap the part of the wall of the furnace which is adjacentto the lower edge of the opening 3.

There can be three or four arms 12, or more, depending on the length ofthe pipe T to be carried.

One of the arms 12, at right angles to the shaft 21, is integral withone of the ends of an actuating arm 14, which is short and rectilinear.The arm extends from the other end of the shaft in relation to the arm12 and is articulated at 26 to the end of the stem of the actuator 15.The actuator housing is jointed at 27 on a supporting flange or lug 16which is attached to the external face of the wall of the furnace 1.

Lateral rails 17 which define a part-circular rolling surface which isconcentric to the wall of the furnace, are embedded in the refractorybrickwork 2 of the furnace for the purpose of receiving pipes T insidethe furnace and within the bath M. The rails 17, which, in the centredposition shown in FIG. 1, extend symmetrically either side of the planeP, are raised at their end at 17a to form stops for the pipe T whichrolls on the rails 17. The arc of the rail 17 corresponds to the maximumamplitude of rotation of the annealing furnace 1 and determines thediameter of pipe which can be treated within the furnace. For largediameters the amplitude of the arc must increase in order to make itpossible for the pipes to make at least a half turn in each direction ofrotation of the furnace. For a pipe of small diameter the amplitude andthe arc of the rails 17 can, on the other hand, be reduced.

In order to make it possible for the cradles 24, when loaded with apipe, to move below the level of the rails 17 at the end of a returntravel of the arms 12, in order to place the pipe on the rails 17, ahollow 18 is provided in the refractory lining 2, between the rails 17,in order to receive the end part of the arms 12.

By means of this installation the annealing of a cast iron pipe T, withspheroidal or lamellar graphite, or a steel tube T is carried out, indifferent phases, in the following manner.

It is assumed that the furnace 1 is stopped. Since its cover 4 isretracted, its opening 3 is directed towards the upper rolling ramp C.The rectilinear outside edge 23a of the branch 23 of the arms 12 is inthe extension of the ramp C (FIG. 1), in a position in which the endcradles 24 form stops for a pipe T. The actuator 16 immobilises them inthis position for receiving a pipe T. The furnace 1 contains a metalbath M which is kept molten by the burners 5, whose level is clearlylower than that of the lower edge of the opening 3 which must be loweredeven further during the course of a further rotation of the furnace.

A pipe T rolls on the ramp C in the entry direction D, it engages on thearms 12 until it comes to a stop against the cradles 24 of the arms 12which hold it. The actuator 15 then causes the arms 12 to tilt in such amanner that the pipe T is brought nearer to the opening 3 of the furnaceand introduced inside.

To make this introduction easier, the reduction gear unit 10 is set inoperation so that simultaneously with the rocking of the arms 12, thefurnace 1, which is carried by its annular bearing surfaces 6 on therollers 7, turns in the direction of the arrow f. The end of theinternal rails 17, which is adjacent to the lower edge of the opening 3,is thus lowered, the purpose of this rotation of the furnace,coordinated with the rocking of the arms 12, being basically to preserveat every moment a perfectly balanced position of the pipe T on the arms12, avoiding too sharp a slope of the branch 23 of the arms 12 fromrisking causing the pipe to roll by gravity above the end of the cradles24 and to be caused to plunge suddenly into the annealing furnace. Thepipe T thus approaches the rails 17 following a trajectory of obliquedirection G (FIGS. 1 and 4).

Before the furnace 1 has reached the limit of its rotation in thedirection f and before the lower edge of the aperture 3 has reached itslowest position, the arms 12, by means of rocking, assume a more tiltedposition whilst still keeping the pipe T firmly supported. The pipe issatisfactorily retained because of the concave shape of the cradles. Thepipe T begins its immersion in the bath M.

At the end of the angular travel of the furnace 1, when the hollow 18 ismore or less centred in relation to the plane P, the arms 12 havereached their furthest tilting position around the shafts 21. At thismoment the cradles 24 are retracted below the rails 17, into the hollow18, in such a manner that the pipe T is placed gently on the rails 17(FIG. 4), in a gravitationally balanced position for which its axis isin the plane P. In this example, the pipe T is not totally immersed orsubmerged, one part of its cross section remaining outside the bath M,but if its diameter was sufficiently small, it would be completelyimmersed.

After the pipe T has been deposited on the rails 17 the direction ofrotation of the reduction gear unit 10 is reversed, and hence that ofthe furnace 1, which then turns integrally with the arms 12 which arecompletely returned, in the direction f₁ in such a manner that the pipeT, which remains practically centred in the plane P, rolls on the rails17 and is placed outside the reach of the cradles 24 of the arms 12. Itis then possible for the arms 12 to be removed from the furnace by atilting movement being imparted to them in clockwise direction, by meansof the actuator 15, which saves them from thermal stresses of longduration and makes it possible to close the cover 4 (FIG. 5).

The heat treatment of the pipe T is carried out with the cover 4 closed,under the influence of a reciprocal movement of rotation of the furnace,that is, angular oscillations in the two directions f and f₁, with thearms 12 outside the furnace. During each travel in the direction f or f₁the pipe T remains practically centered in the plane P, but it turns onitself as it rolls on the rails 17 in bath M in which its annealing iscarried out in this manner. At each end of travel of the furnace thepipe comes to a stop on the turned up end part 17a of the rails 17.

During the process of the oscillations, the pipe T rolls progressivelyimmersing the whole of its cross section in the bath M. If, as in thisexample, it is never completely immersed owing to its diameter beinggreater than the greatest depths of the bath, the amplitude of the arcsof the circle formed by the rails 17 is sufficient to make it possiblefor the pipe T to accomplish a complete revolution on rolling in orderto soak the whole of its circular cross section. Whatever the diameterof the tube T may be, its rolling action on the rails 17 avoids itsbecoming oval.

When the annealing time has elapsed, without stopping the oscillationsof the furnace, the cover 4 is open in order to free the opening 3completely, and, at a moment at which the end of the rails 17 oppositethe opening 3 is under the pipe T, the actuator 15 is activated again insuch a manner as to cause the arms 12 which follow the direction G totilt in the furnace, the cradles 24 resuming their retracted position inthe hollow 18 under the rails 17. (FIG. 7).

At the end of the next oscillation, in the direction f of the furnace,the cradles 24 come underneath the pipe T and the furnace, whoseposition is then such that the lower edge of the opening 3 is at itsnearest position to the lower rolling ramp C₁, is stopped. The arms 12are raised by means of the actuator 15, following the oblique trajectoryG₁ (FIG. 8), and they raise the pipe T. The tilting movement of the arms12 can then be stopped, at the moment at which the linear edge 23a ofthe branch 23 of the arms 12, which is situated in the extension of thelower rolling ramp C₁, is sufficiently tilted for the pipe T to be ableto roll onto this edge and in this manner to reach the evacuation rampC₁, possibly aided by the thrust exerted by the concavity formed by thecradles 24.

The arms 12 can be of a slightly different shape from that of FIGS. 1and 9, provided that they have a loop 22 in order to avoid the wall ofthe furnace and an end cradle.

In FIG. 11 the arm 12a has elbows with obtuse angles instead of havingcontinuous curves. The end cradle 24 forms an obtuse angle or a flaredV.

In the variant of the arms 12b of FIG. 12 the end cradle constitutes asimple elbow of about 90°, which projects slightly in relation to thelinear branch 23. This form of execution is suitable for pipes T ofsmall diameter.

In FIG. 13, the variant of the arm 12c includes a turned up end elbow.

It is possible to provide several actuators 15, which are obviouslysynchronized, for the control of the arms 12, whose number, as hasalready been indicated, can be greater than two.

According to the variant of FIGS. 9 and 10, the hollow 18 is eliminatedand the rails 17 have a projecting height above the refractory wall 2which is greater than the thickness of the cradled end 24 of thegripping arms and support arms 12 of a pipe.

Owing to the coordination, which is obtained by known means, of thesimultaneous movements of rotation of the furnace 1 and tilting of thearms 12, and owing to the tilting of the trajectories G and G₁, the pipeT is supported by the cradles 24 of the arms 12 in a position of perfectequilibrium at the moment that it is introduced (FIG. 4), and removed(FIG. 8) without the risk of escaping from the arms 12 and fallingsuddenly into the bath M. This same coordination of the two movements ofrotation around the axis XX and the axis YY, which rotates about theaxis XX, makes it possible to place the pipe T gently on the rails 17,at the bottom of the furnace, in a position which is balanced and stable(FIGS. 4 and 10).

Owing to the hollow 18 which is situated axially to the right of one ofthe ends of the rails 17, the cradle ends of the arms 12 can place apipe T on the rails 17 and take it up again. The hollow 18 makes itpossible to limit the projection of the rails 17 above the wall of therefractory lining 2 and consequently gives the benefit of a greateruseful volume in the furnace 1.

On the other hand, the variant of FIGS. 9 and 10 in which the hollow 18is eliminated and replaced by a greater height of the rails 17, has theadvantage of facilitating the making of the refractory lining wall 2 buthas the drawback of reducing the capacity of the content of the furnace1.

By means of the rails 17 and the rotations of the furnace 1 in theopposite directions f and f₁, the pipe T rolling on the rails 17 turnson itself 180° in both directions, thus achieving a complete revolution,and avoids becoming oval whilst soaking the whole of its lateral crosssection during the course of its rotation, even if its diameter isgreater than the depth of the bath. Because of the shape with multiplecurves or elbows of the arms 12, 12a, 12b, and their hinging onto thefurnace 1 itself, and their pivoting assembly, each pipe T is easilytransferred in both direction D - G, D₁ -G₁ between the supply andremoval ramps C, C₁ and the rails 17 of the furnace, in a stable andbalanced position, without risk of escape and falling, hence, followingthe shortest trajectory, and with the greatest safety. The possibility,afforded by the rotation of the furnace 1, of bringing the opening 3close to the rolling ramps C and C₁ also contributes to this advantage.

Finally, because of the tilting of the arms 12 around shafts 21 carriedby lugs 11 fixed to the furnace, it is possible to hold the arms 12outside the furnace during the heat treatment and thus to reduce theirwear, and it is possible to close the cover of the furnace, and hence toimprove its heat insulation.

Although this has not been shown, the furnace 1 can be provided with atleast one lateral opening for introducing a suitable powder into themetal bath M with a view to preventing the aluminium from adhering tothe pipe. This powder can be carbon black. It can be projected onto theinside and outside of the pipe T and inside the furnace 1.

According to FIG. 14, the external means of gripping and support of eachpipe T does not have to be made integral with the furnace 1. In thisvariant the furnace 1 remains rotating and oscillating and consists onthe inside of rails 17 for rolling of the pipe T. Each pipe T is simplyplaced on the rails 17 and taken up from these rails 17 after heattreatment, by means of hooks 19 which pass under the lower surface ofthe pipe T. These hooks 19 with curved ends are suspended from a liftingapparatus, for example, symmetrically to the vertical plane P whichpasses through the axis XX of rotation of the furnace 1.

Of course, the system for causing rotation of the furnace 1 and thesystem for tilting the arms 12 described above can again be replaced byequivalent systems.

As a variant, one could have only one rolling ramp C, situated in theupper position, from which each pipe is introduced into the furnace,this ramp remaining free until the pipe is removed from the furnace inorder to bring it back onto the same ramp with a view to its removal. Inthis case the rotation of the furnace is carried out in one direction,at the same time that the rocking of the arms 12, in order to introducethe pipe into the furnace is carried out in the opposite direction, in asymmetrical manner, to remove the pipe from the furnace.

We claim:
 1. An installation including a furnace of a generallycylindrical shape, containing a treatment bath of molten metal, meansfor heating the treatment bath, rollers for rotatably supporting thefurnace wherein the furnace is rotatable around a longitudinal axis ofsaid furnace, handling means for introducing and removing pipes throughan opening in the furnace, and means for imparting an angular movementto the furnace around its longitudinal axis, characterised in that, onthe internal wall of the furnace, rolling surfaces are provided whichare directed laterally and are of concave profile, for supporting a piperesting thereon, and wherein the handling means comprise means forretaining and transferring a pipe, the retaining and transferring meansbeing articulated on an external wall of the furnace in such a mannerthat they can penetrate within the furnace in order to place a pipe tobe treated on rolling surfaces of the furnace and can be moved out ofthe furnace in order to remove a treated pipe from the bath.
 2. Aninstallation according to claim 1, characterized in that the rollingsurfaces consist of rails in the form of an arc of a circle whose centeris on the axis of the furnace.
 3. An installation according to claim 2,characterised in that the rails are turned up at their ends to formstops with regard to the pipe.
 4. An installation according to claim 1,characterised in that the retaining and transferring means comprise atleast two arms, each of which is pivoted at one of its ends to theexternal face of the wall of the furnace, each arm being pivoted aboutan axis which is parallel to the axis of the furnace and having a curvedconfiguration defined by a loop one of whose branches is adjacent to thepivot axis, an end part in the form of a cradle, and a central portionwhich is a continuation of the end part and is connected to the loop,whereby a pipe can be retained in the end part and moved into thefurnace through an opening to a final position in which the loopdescribes a curve around the part of the wall of the furnace which isadjacent to the corresponding edge of the opening and the pipe is placedon the rolling surfaces.
 5. An installation according to claim 4,characterised in that the rolling surfaces form, in relation to therefractory lining of the furnace, a projection whose dimension isgreater than the thickness of the cradle defining end part of the arms.6. An installation according to claim 4, characterised in that therefractory lining of the furnace consists of at least one recess whosedepth is such that the cradle end of the arms, engaged in this hollow,is retractable to a level lower than the rolling surfaces.
 7. Aninstallation according to claim 4, characterised in that, in order tocontrol the pivoting movement of the arms, at least one actuator isprovided whose moving element drives an actuating arm integral with thearms, the actuating arm being situated on the opposite side of the pivotaxis to the arms.
 8. An installation according to claim 4, characterisedin that the loop and the cradle defining end part are formed as concavecurves in the arms.
 9. An installation according to claim 4,characterised in that the loop and the cradle defining end part areformed as elbows of the arms.
 10. An installation according to claim 2,characterised in that the opening of the furnace can be closed by amovable cover when the arms are outside the furnace.
 11. An installationaccording to claim 4, characterised in that the edges of the centralportions of the arms, which are continuations of the cradle defining endparts, are approximately linear in such a manner that they can besituated in the extension of a supply ramp which is outside the furnace,on which the pipe can roll before being retained on the cradle.
 12. Aninstallation according to claim 11, characterised by an evacuation rampwhich is situated outside the furnace at a level lower than that of thefeed ramp and on which a pipe can be placed by the arms after itstreatment.